Ultrasonic cleaning method and apparatus



Dec. 7,1965 so 3,222,221

ULTRASONIC CLEANING METHOD AND APPARATUS Filed-April 29, 1959 INVENTORJWnmarz .Branson ATTORNEYS United States Patent 3,222,221 ULTRASONICCLEANING METHOD AND APPARATUS Norman G. Branson, Revonah Woods,Stamford, Conn,

assignor, by mesne assignments, to Branson Instrumerits, Incorporated,Stamford, Conn., a corporation of Delaware Filed Apr. 29, 1959, Ser. No.809,718 5 Claims. (Cl. 1341) This invention relates to a method andapparatus for ultrasonic cleaning of small articles and particulatematerials. More particularly, it relates to the cleaning by ultrasonicmeans of sand, grinding wheel particles, tumbling media, ball bearings,nuts and bolts, and all other small articles and small machine parts.

There has been developed in the past ten years a Whole new technology ofcleaning using the effects produced by so-called ultrasonic energy.Generally, sonic vibrations ranging in frequency from kilocycles to 1megacycle have been used for ultrasonic cleaning of the surfaces ofobjects. Sonic vibrations of approximately 20 kilocycles, which is justabove the range of audibility for most persons, have been found to beeffective for many surface cleaning operations.

In ultrasonic cleaning, a sonic field is set up in a liquid cleaningmedium and the objects to be cleaned are introduced into the medium;where the cleaning action takes place at their surface. It is believedthat cavitation, caused in the liquid medium by the extreme pressuredifferentials produced in the medium by the ultrasonic waves, causes thecleaning action. It has been discovered that the cavitation bubbles aremore likely to form around small nuclei in the liquid or on the surfacesof objects in the liquid and that these bubbles or cavities may be madeto form and then to implode during one complete pressure cycle of anultrasonic wave. It has also been found that caviation will occur inliquids from induced sonic fields having frequencies ranging from 3kilocycles to 2.5 megacycles. The present invention, althoughparticularly directed to the preferred 20 kc. frequency now used, isapplicable to the full range of ultrasonic cleaning frequencies.

When an object is introduced into the ultrasonic field in an ultrasoniccleaning medium the cavitation bubbles form at and around the surfacecontaminants and the contaminants seem to literally explode off thesurfaces of the object. Various other chemical reactions have been foundto be accelerated by the application of ultrasonic energy to chemicalreagents. The use of a combined chemical reaction and ultrasonic fieldfor cleaning the surfaces of objects is disclosed in the co-pendingapplication of Frank W. Hightower and Walter J. Bleistein Serial No.645,477, filed March 12, 1957, now Patent No. 3,033,710 relating toMethod and Apparatus For Surface Cleaning Using Ultrasonic Energy, andassigned to the same assignee as the invention herein.

It has been one of the anomalies of the ultrasonic art that many of theobjects and materials to which application of ultrasonic cleaning ismost desirable have in the past not lent themselves to the existingmethods of ultrasonic cleaning. In particular, it is most desirable thatsand and other hard particulate materials should be cleaned byultrasonic methods. When such materials are used in the manufacture ofgrinding wheels, any impurities or contaminants left in the materialwill interfere with the bonding of the particles together into thegrinding Wheel units, and such poor bonding has sometimes in the pastcaused the wheels to explode, thus presenting a danger to operators andto machines using the grinding wheels. Also, when sand, gravel, metalscraps, etc., are

Patented Dec. 7, 1965 used as tumbling media for debnrring, boning andpolishing, it is desirable that these media should be capable of beingcleaned by ultrasonic methods. The characteristics of the tumbling mediaare adversely affected by the vari ous particles, grease and othercontaminants removed during the tumbling process. The presentnon-ultrasonic, chemical and agitation, cleaning methods have provedinsufficient to properly clean these materials for re-use. Theapplication of ultrasonic cleaning methods to such materials providesthe opportunity for complete cleaning so that the materials may bere-used.

Ultrasonic cleaning methods have been somewhat imperfectly applied tothe cleaning of ball bearings for high precision machines, such asgyroscopes, in which it is absolutely necessary that all contaminants beremoved from the bearings and associated small parts in order for themachine to properly operate over a reasonable lifetime. Nuts and boltsfor such high precision machines must also be perfectly clean;otherwise, the use of contaminated nuts and bolts may introduce into themachine contaminants which would adversely affect the lifetime andoperation of the device. The same is true for all small parts in highprecision machinery, and to some extent for small parts for use in anymachines which are contaminated during the manufacturing process.

In the prior art the methods of treating small parts and particulatematerials have been two in number. The cleaning of ball bearings andother small parts for high precision machines can be done on anindividual basis, if only a few of such machines are to be built. Thisof course is impratcical for any high volume production. If largequantities of small parts and particulate materials are desired to becleaned by the ultrasonic methods of the prior art, a batch of suchmaterial is placed in the sonic field, in an ultrasonic medium, and thebatch is occasionally stirred. By this technique the parts or particlesnear the outer surfaces of the batch are cleaned ultrasonically butthose in the middle are not subjected to ultrasonic caviation, whichcauses the cleaning, because the sound intensity is too low at themiddle of the batch, having been attenuated by its passage through theouter portions of the batch. Also, air and other gases collect on thesurfaces of the material being cleaned due to the cavitation processand, in a batch, this gas is prevented from escaping. Cavitation nolonger occurs on those surfaces to which the gas attaches itself, andcleaning stops there. Dirt and other contaminants are caught in thecenter of the batch since the flow of the cleaning liquid through thebatch is inhibited, thereby preventing the removal of free dirt andcontaminants. This inhibited fluid motion also reduces the action ofsolvents, acids or other chemicals used in combined chemical andultrasonic cleaning. The above problems of the prior art batch cleaningmethod are eliminated when large parts are cleaned, or when small partsare cleaned on an individual basis, since all surfaces of the object canbe subjected to ultrasonic energy in the ultrasonic medium. The methodand apparatus of the present invention solves these problems of theprior art in cleaning small articles and particulate materials by doingso on a semi-individual basis,

thus allowing the cleaning of large volumes of material.

It is therefore an object of this invention to clean small parts andother small articles by ultrasonic methods. Another object of theinvention is to clean particulate materials by ultrasonic methods. Afurther object of the invention is to clean small parts, small articlesand particulate materials ultrasonically on a semi part-bypart,article-by-article or particle-by-particle basis. A still further objectof the invention is to accomplish the above objects in a continuousprocess.

Another object of the invention is to provide means for placing eachpart, article or particle into a sonic field for cleaning individually.Yet another object of the invention is to accomplish objects of theabove character in such a way that each part, article or particle is intotal contact with the ultrasonic cleaning fluid when it is in theultrasonic field. Still another object of the invention is to accomplishobjects of the above character and rovide a continuous flow of cleaningfluid around each part, article or particle during cleaning. Anotherobject of the invention is to permit the continuous free escape of gasformed on the surfaces of parts, articles or particles while they arebeing cleaned. Still another object of the invention is to accomplishobjects of the above character and to subject all of the surfaces ofeach part, article or particle being cleaned to direct sonic vibrations.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others, and theapparatus embodying features of construction, combinations of elements,and arrangements of parts, which are adapted to effect such steps, allas exemplified in the following detailed disclosure, and the scope ofthe invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing, in which:

FIGURE 1 is a cross sectional side view of an apparatus adapted toultrasonic cleaning according to the method of the present invention;

FIGURE 2 is a partial top view of the apparatus of FIGURE 1; and,

FIGURE 3 is a top view of a portion of the apparatus of FIGURE 1,showing a modification in the ultrasonic transducer configuration.

Similar reference characters refer to similar parts throughout theseveral views of the drawing.

In general, according to the method of the present invention forcleaning small articles and particulate materials, the particles, partsor articles are introduced into a bath of ultrasonic cleaning fluid,preferably at a constant rate, and allowed to fall freely in the medium,tumbling as they do, through the ultrasonic field in the medium wherethey are subjected to surface cavitation over their entire surface dueto the random nature of their tumbling and falling motion.

More particularly, referring to FIGURES 1 and 2, an apparatus forcleaning sand, gravel, grinding wheel particles and the like comprises atank containing an ultrasonic cleaning fluid 12 which may be anyconvenient solvent or other chemical reagent. The cleaning fluid 12 iscontinuously circulated in the tank 10, entering through inlet 14 at thebottom of the tank and exiting from the top of the tank through theoutlet 16. The used cleaning fluid may be filtered, distilled or treatedin any other convenient manner to remove the impurities which it hastaken up during the cleaning process and may then be reused. Theplacement of the outlet 16 at the top of the fluid level in the tank 10allows any accumulated scum on the surface of the cleaning fluid 12 tobe rather quickly drained off through the outlet 16.

There is contained within the tank 10 a vertically aligned chute 18 ofgenerally parallelopiped construction. The chute 18 is supported withinthe tank 10 by supporting bracket structures 2020 which are mounted onopposite side walls 21 and 23 of tank 10. A number of electro-acousticaltransducers 22 are mounted on opposite walls 15 and 17 of the chute 18.The transducers 22 are driven by an ultrasonic generator (not shown) andacoustically coupled to the walls 15 and 17 for transmission ofultrasonic energy through the walls into the central portion 19 wherethe ultrasonic energy is concentrated. The transducers 22 may beelectrostatic, piezoelectric, or magnetostrictive and are constructed ina manner well known in the prior art.

A continuous endless conveyor belt 24 operates from below the chute 18to the upper edge of the tank 10, as shown in FIGURE 1. The belt 24passes over and around horizontally disposed roller 26 which isrotatably mounted in bushings 27 and 29 affixed to opposite walls 21 and23 of tank 10. As shown in FIGURE 2, the belt 24 passes under and isbent around four parallel horizontally disposed guide rollers 30 andproceeds upwardly in a diagonal direction to a terminal roller 32 whichis mounted above the fluid level on end wall 33 of tank 10. Rotarymotion is imparted to belt 24 by driving roller 32 by means of shaft 28.Upstanding portions 34 along the belt 24 are spaced at equal intervalsand faciliate the transport of fine material diagonally upwards towardsthe terminal roller 32. The material leaving the belt 24 at the terminalroller 32 is deposited on the chute 36 which directs it to the nextoperation. When the apparatus is used to clean fine particulate materialsuch as sand and the like, the belt 24 is chosen to be impervious to thepassage of such material through it and preferably is a non-porouswebbing. When machine parts or other aggregations of larger objects arecleaned the belt 24 is a fine mesh webbing so that any fine impuritieswill fall through it and not be carried to the next operation.

Above the transducer chute 18 there is located a storage bin 38 and aconstant feed mechanism 40. The constant feed mechanism 40 feeds aconstant flow of material to above the transducer chute 18 and may be ofthe wellknown vibrator type. The material 42 which is to be cleaned maybe pre-wetted in the storage bin 33 to facilitate its sinking throughthe surface level 44 of the cleaning fluid 12 above the chute 18 or itmay be introduced into the fluid 12 just below the surface level 44 toprevent suspension of the material 42 by surface tension on the surface44.

The surface level 44 of the cleaning fluid 12 is preferably arranged tobe slightly above the top of the chute 18 so that any accumulated scumis allowed to escape from the chute and pass through the outlet 16. Avertical barrier wall .-6 is mounted between opposite tank walls 21 and23, extends above the belt 24 and above the cleaning fluid levelseparating the surface 44 above the chute 18 from the surface 45 throughwhich the belt 24 passes and prevents scum accumulating on the surface44 from spreading to the surface 45 through which belt 24 passes, thuspreventing scum from being deposited on the cleaned material as itpasses upwardly through the liquid surface.

As is well known in the ultrasonic art, the arrangement of theelectro-acoustical transducers 22 along opposite sides of the transducerchute 18 as shown in FIGURES 1 and 2 will produce a substantiallyuniform sonic field within the chute 18. If higher sonic intensities are(esired at the surfaces of the material to be cleaned, the transducersmay be arranged to focus their energy as shown in FIGURE 3. In thiscircular arrangement, the tranducers 22 are arranged within a chute ofcircular cross section 48. The transducers 22 are coupled at their innerfaces 50 directly to the ultrasonic fluid 12 within the chute 48 and thearrangement of the transducers 22 produces a focusing effect whereby theultrasonic intensity within the chute is greatest at its center. When achute of this nature is used the stream of falling material 42 shouldpreferably be restricted to a relatively narrow stream through thecentral portion of the chute, where the ultrasonic energy isconcentrated.

The apparatus shown in FIGURES 1 and 2, with or without the modificationshown in FIGURE 3 operates substantially as follows. The material 42 tobe cleaned, which in this example is sand, gravel, or other fineparticulate material, but with minor modifications of the apparatus maybe any aggregation of small objects, or

other aggregative material, is constantly dropped into the ultrasoniccleaning fluid 12. The material then freely falls, tumbling in a randomway, through the chute 18 (FIGURES 1 and 2) where it is subjected tosurface cavitation caused by the ultrasonic field of energy, produced bythe transducers 22. This cavitation causes the entire surface of eachindividual particle or part of the material to be thoroughly cleaned.After passing through the chute 18, the material is caught on theconveyor belt 24 and is carried out of the tank and deposited onto thechute 36. The material is partially subjected to some rinsing action asit is drawn through the cleaning fluid 12 by the belt 24. The cleaningoperation may be performed several times using a plurality of cleaningtanks as heretofore described.

It will be obvious to anyone skilled in the ultrasonic cleaning art thatthe crux of the method herein described is allowing each part, articleor particle which is to be cleaned to free fall in a tumbling mannerthrough an ultrasonic cleaning field, so that all surfaces of each part,article or particle will be subjected to ultrasonic cavitation. Manyvariations of apparatus for practicing the method of the invention willoccur to persons skilled in the art; for example, the material to becleaned may be mixed with the ultrasonic cleaning fluid and sprayedhorizontally out of a nozzle through an ultrasonic cleaning field; or toclean material which is less dense than the liquid and hence will floatin the ultrasonic cleaning fluid, provision may be made for introducingsuch material into the bottom of the vessel and allowing the material tofloat to the surface of the fluid through an ultrasonic cleaning field.Therefore, in the following claims the terms free fall or freely fallingare intended to mean any free unsupported motion through an ultrasoniccleaning field.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efliciently attained, and,since certain changes may be made in carrying out the above method andin the constructions set forth without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawing shall be interpreted asillustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secureby Letters Patent is:

1. A method for removing contamination from small objects comprising thesteps of dropping said objects into a solvent for the contamination,permitting said objects to fall freely through said solvent, andultrasonically activating said solvent to the degree necessary to causecavitation in the solvent as the objects fall through it.

2. A method for cleaning the surface of particulate elements, saidmethod comprising the steps of introducing said elements below thesurface of a sonic cleaning liquid, said elements having a density lessthan the density of said liquid, permitting said elements to risethrough said liquid toward the surface thereof, and ultrasonicallyactivating said liquid to the degree necessary to cause cavitation inthe liquid as the elements rise through it.

3. The method of cleaning particulate elements which comprises droppingsaid elements into a sonic cleaning liquid, permitting said elements tofall freely through said liquid, and ultrasonically activating saidliquid to the degree necessary to cause cavitation in the liquid as theelements fall through it.

4. The method of removing oil from oil bearing elements which comprisesdropping said elements into a solvent for oil, permitting said elementsto fall free through said solvent, and ultrasonically activating saidsolvent to the degree necessary to cause cavitation in the solvent asthe elements so fall through it.

5. Apparatus for cleaning aggregative material comprising, incombination, a tank for containing cleaning fluid, a plurality ofultrasonic transducers to create a field of ultrasonic energy in avertical portion of the cleaning fluid in said tank, said plurality ofultrasonic transducers vertically and oppositely positioned in said tankto subject materials in said vertical portion to ultrasonic energy fromat least two directions, and means for dropping a stream of theaggregative material into said portion of the cleaning fluid above saidfield of ultrasonic energy whereby the material freely falls duringcleaning under the influence of gravity through said ultrasonic field ofenergy.

References Cited by the Examiner UNITED STATES PATENTS 898,954 9/1908Baker 134-73 1,544,894 7/1925 Farnsworth 134-25 X 1,580,723 4/ 1926Hapgood 134-25 X 1,791,797 2/ 1931 Clark 208-11 2,460,919 2/ 1949Bodine. 2,578,505 12/ 1951 Carlin. 2,620,894 12/ 1952 Peterson.2,635,614 4/1953 Ford 134-74 X 2,722,498 11/ 1955 Morrell et a1. 208-112,735,795 2/1956 Weiss 134-25 2,742,408 4/ 1956 La Porte 208-1462,845,936 8/ 1958 Boynton 134-25 X 2,871,180 1/1959 Lowman et al. 208-112,919,215 12/1959 Neuhaus 134-1 2,972,997 2/1961 McCown 134-1 X2,973,312 2/ 1961 Logan.

FOREIGN PATENTS 1,011,301 4/1952 France. 1,052,776 3/ 1959 Germany.

MORRIS O. WOLK, Primary Examiner.

SIDNEY JAMES, CHARLES A. WILLMUTH, AL-

PHONSO D. SULLIVAN, MILTON STERMAN, DONALL H. SYLVESTER, Examiners.

1. A METHOD FOR REMOVING CONTAMINATION FROM SMALL OBJECTS COMPRISING THESTEPS OF DROPPING SAID OBJECTS INTO A SOLVENT FOR THE CONTAMINATION,PERMITTING SAID OBJECTS TO FALL FREELY THROUGH SAID SOLVENT, ANDULTRASONICALLY ACTIVATING SAID SOLVENT TO THE DEGREE NECESSARY TO CAUSECAVITATION IN THE SOLVENT AS THE OBJECTS FALL THROUGHT IT.
 5. APPARATUSFOR CLEANING AGGREGATIVE MATERIAL COMPRISING, IN COMBINATION, A TANK FORCONTAINING CLEANING FLUID, A PLURALITY OF ULTRASONIC TRANSDUCERS TOCREATE A FIELD OF ULTRASONIC ENERGY IN A VERTICAL PORTION OF THECLEANING FLUID IN SAID TANK, SAID PLURALITY OF ULTRASONIC TRANSDUCERSVERTICALLY AND OPPOSITELY POSITIONED IN SAID TANK TO SUBJECT MATERIALSIN SAID VERTICAL PORTION TO ULTRASONIC ENERGY FROM AT LEAST TWODIRECTIONS, AND MEANS FOR DROPPING A STREAM OF THE AGGREGATIVE MATERIALINTO SAID PORTION OF THE CLEANING FLUID ABOVE SAID FIELD OF ULTRASONICENERGY WHEREBY THE MATERIAL FREELY FALLS DURING CLEANING UNDER THEINFLUENCE OF GRAVITY THROUGH SAID ULTRASONIC FIELD OF ENERGY.